This invention relates to lamps aid more particularly to high intensity discharge lamps. Still more particularly, it relates to a frame assembly for supporting a mount structure within a lamp envelope.
High intensity discharge lamps are known and are well used because of their high light output and favorable energy demands. Such lamps employ as a light source an arc tube of quartz or similar heat resistant material in which an arc is generated to form a heated plasma which provides the illumination. Often, these arc tubes are surround by a shroud or shield to contain shards in the unlikely event of an arc tube catastrophic failure. As light sources, these arc tube and shield assemblies are very heavy when compared to the almost insignificant weight of, for example, the tungsten filament of an incandescent lamp. Accordingly, it is the generally accepted procedure in the lamp industry to mount the arc tube assembly such that it is held in place by structures at both the top and bottom of the lamp envelope. The bottom mounting arrangements are generally easier to handle because of the flare and pinch seal available at the bottom of the lamp, as well as the availability of the relatively substantial in-leads. Securing the mount structure to the top of the lamp envelope has proven to be more of a problem, caused primarily by the rather large tolerances permitted in many lamp envelopes. Techniques have included multiple springs as shown in U.S. Pat. No. 5,065,069, a dimple and rig arrangement, shown in U.S. Pat. Nos. 5,327,042 and 4,963,790, and snubbers, such as shown in U.S. Pat. No. 4,801,846. While all of the above-cited techniques have been employed, problems persist because of excess cost (the multiple spring arrangement), problems with envelope breakage (the dimple and ring) and costs involved in manually adjusting the snubbers to accommodate the differing envelope sizes caused by the rather large tolerances permitted, the latter technique often requiring a mount to be inserted and withdrawn multiple times before the correct tension is achieved.
It is, therefore, an object of this invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a stable arc tube mount that will accommodate differing diameters occurring in lamp envelopes.
These objects are accomplished, in one aspect of the invention by the provision of a high intensity discharge lamp comprising: an outer envelope having a cup-shaped top, a hollow center section and a bottom all aligned along a longitudinal axis, the bottom including a flare having a pinch seal with in-leads sealed therein; and a mount structure within the envelope, the mount structure including a frame comprising a spaced-apart pair of side frames extending substantially the length of the envelope and parallel to the longitudinal axis, the side frames having middle portions carrying an arc tube and a surrounding shield, the side frames further comprising an upper portion that frictionally engages the inside surface of the cup-shaped top, the upper portion comprising two ends extending in a direction normal to the longitudinal axis and having a space therebetween.
The two ends extending toward one another provide a spring-effect that holds the mount in position. Further, the amount of movement capable between the two ends accommodates the great variation that can occur in the inside diameter of the upper portion of the lamp envelope.